Just out of carosity, what are you trying to power? Plug configurations are to prevent applying the wrong voltage, improper ampere, and in this case, possibly the wrong frequency. By installing a receptacle of a certain configuration invites any type of equipment with that plug configuration be plugged into it. Even in an supervised environment. If you are installing a piece of European equipment that will work on the North American power grid, can't you just install the appropriate plug and recept configuration?
I was figuring that if they were made for wall mounting, they would more likely be made to fit in a decora style plate, rather than the traditional ones. E.g. a single device with one, two, or maybe even three, C13 outlets, in the decora dimensions.